Theory of neutral and charged exciton scattering with electrons in semiconductor quantum wells

Electron scattering on both neutral ($X$) and charged ($X^-$) excitons in quantum wells is studied theoretically. A microscopic model is presented, taking into account both elastic and dissociating scattering. The model is based on calculating the exciton-electron direct and exchange interaction matrix elements, from which we derive the exciton scattering rates. We find that for an electron density of $10^9 {\rm cm}^{-2}$ in a GaAs QW at $T=5K$, the $X^-$ linewidth due to electron scattering is roughly twice as large as that of the neutral exciton. This reflects both the $X^-$ larger interaction matrix elements compared with those of $X$, and their different dependence on the transferred momentum. Calculated reflection spectra can then be obtained by considering the three electronic excitations of the system, namely, the heavy-hole and light-hole 1S neutral excitons, and the heavy-hole 1S charged exciton, with the appropriate oscillator strengths.Comment: 18 pages, 12 figure

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Not AvailablePermanent structures are being used traditionally to stabilize the slopes in hill region which is tedious and costly process. As the slope failure is result of land slide, mining, flood, etc, slope stabilization using permanent structures cannot be adopted in larger scale. Slope stabilization by establishing vegetation with the support of Jute Geotextiles is an alternative method for stabilization of slopes in hilly areas. Set of field studies have been conducted at ICAR- Indian Institute of Soil and Water Conservation (IISWC), Regional Centre, Udhagamandalam, Tamil Nadu, India with the objective to study the effect of various Jute Geotextiles (JGT) on runoff, soil loss, survival and growth of tea. The results shows that the 500 GSM Open Weave Jute Geotextiles is effective in reducing runoff (6.7 - 12.5%), soil loss (3.93 t-1ha-1yr-1) and nutrient loss (46 - 62%) and recommended for hill slope stabilization and reclamation of land slide affected areas using tea plants. Similarly, 700 GSM Open Weave Jute Geotextiles with grass reduced runoff (3.5 - 7.7%) soil loss (2.4 t-1ha-1yr-1) and nutrient loss (55.7%). As per BIS (Bureau of Indian Standard), 730 GSM open weave jute goe-textiles is recommended for hill slop stabilization using grass species up to 90 percent slope. Grass/hedge crop establishment with jute geo-textiles can also help to environmentally sustainable landscape development in airports, parks and housing estates. It is also proved that the mass eroded land and areas affected by natural calamities can be rehabilitated by vegetation establishment using jute geo-textile. Thus, it is the high time to review the policy interventions in all developmental activities of various departments to include the vegetation establishment using jute geo-textiles as an eco-friendly slope stabilization measures. SlopeNot Availabl

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Not AvailableMeeting the food grain demand of ever growing global population is the big challenge to agriculture sector. Plant disease significantly reduces the production of food crops besides affecting the quality adversely. Losses associated with plant diseases in yield reduction ranging from slight to catastrophic depending upon varying factors. Literature review highlighted that an average yield loss of 42 % from the six most important food crops. It is vital to manage plant diseases to avoid the yield loss, which helps to meet the food grain demand in simple means. In other way, disease management is helping us to meet the food grain demand of i ncreasi ng populat i on under shrinkage of cultivable area.Not Availabl

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Not AvailableSlope stabilization is a tedious process since various human activities being carried out in various parts of the world have led to land use changes that has indirectly affected slope stability. Permanent structures are being used for slope stabilization which are costly and cannot be adopted in a large scale. Slope stabilization by establishing grasses with the support of Jute Geotextiles is an alternative method for stabilization of slopes in hilly areas. Set of field studies were conducted at ICAR- Indian Institute of Soil and Water Conservation (IISWC), Regional Centre, Udhagamandalam, Tamil Nadu, India with the objective to study the effect of various Jute Geotextiles (JGT) on runoff, soil loss, survival and growth of tea. Results of three years field study on efficacy of various types of open weave JGT namely 500, 600 and 700 GSM on slope stabilization showed that 700 GSM open weave JGT proved to be more effective in reducing runoff, soil and nutrient loss and increased soil moisture retention capacity of the soil. However, height and growth of tea plants were better under 500 and 600 GSM JGT. Considering the scope of tea cultivation in sloppy areas, rehabilitation of land slide areas using tea plants, optimal moisture requirement and better growth of tea plants, it is suggested that 500 GSM open weave JGT will be more effective for slope stabilization with tea plants.Not Availabl

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Not AvailableSoil erosion is increasingly recognized as a problem in hilly regions which needs an effective and economic solution. Slope stabilization in hilly areas is now become a costly and tedious process since various human activities have led to land use changes which have indirectly affected the slope stability. Permanent structures are being used for slope stabilization which are costly and cannot be adopted on a larger scale. On other side, availability of area for construction of permanent structures in the road side is also a major constraint in many locations. Hence growing vegetation in these areas to cover and protect the soil is the wise choice for hill slope stabilization as it is sustainable as well as environmental friendly. However there are certain limitations which can hamper the establishment of vegetation in slopes as it is not able to resist severe scour or high runoff and takes time to establish (Abramson et al., 1995). Without immediate, appropriate and adequate protection, slopes can suffer from severe soil erosion and instability, which in turn makes vegetation establishment extremely difficult. Thus some mechanical protection at initial stage of the vegetation establishment is imperative on steep slopes which resists soil erosion, retains runoff and facilitates establishment of vegetation on the surface. Different ranges of natural and Synthetic Geo-textiles have been used for this purpose. Apart from conventional civil engineering applications, Geosynthetics play a major role even in environmental engineering applications including pollution control, landfills and erosion control. Alternatively natural fibre based Jute Geo Textiles (JGT) are also utilized effectively in road construction and slope stabilization to some extent. Recently, coir Geo-textiles have been evaluated for slope stabilization and rehabilitation of heavy metal contaminated soils. Its natural water absorbing capacity helps to conserve soil moisture and anchor soil firmly in sloppy areas. Keeping in view the erosion control characters of Jute Geo-textiles, two experiments were conducted to compare the performance of Jute Geo-textiles with Synthetic Geo-textiles as well as to identify the suitable Open Weave Jute Geo-textiles for hill slope stabilization with the following objectives. 1. Assess the impact of different Jute and Synthetic Geo Textiles on runoff and soil loss under various slopes. vii 2. Study the growth of tea and grass grown for soil binding under different Geo-textiles. 3. Evaluate the impact of Geo-textiles on soil moisture and nutrient losses. Two sets of field experiments were conducted at the Research Farm of ICAR - Indian Institute of Soil and Water Conservation (formerly known as Central Soil and Water Conservation Research and Training Institute), Research Centre, Udhagamandalam, Tamil Nadu which represents the geographical area of Nilgiris. Effect of different types of Geo-textiles on runoff, soil loss, nutrient loss, soil moisture retention, growth parameters of tea and grass has been evaluated. Results of three years field study on efficacy of various types of Open Weave Jute Geo-textiles namely 500, 600 and 700 GSM on slope stabilization showed that 700 GSM Open Weave JGT is more effective in reducing runoff, soil loss and nutrient loss and increasing soil moisture retention. However, plant height and growth of tea plants were better under 500 and 600 GSM JGT. Higher biomass of grass and other herbs in between tea plants was generated by 700 GSM JGT. Considering the scope of tea cultivation in sloppy regions, rehabilitation of land slide areas using tea plants, optimal moisture requirement and better plant growth of tea plants and economics, it is suggested that 500 GSM JGT will be more effective for slope stabilization with tea plants. Keeping in view of higher biomass production of grass and other herbs grown in between tea plants, 700 GSM JGT will be suitable for slope stabilization with grass. Results of three years field study on efficacy of various types of Jute Geotextiles and Synthetic Geo-textiles on 60 and 90 per cent slopes show that Jute Geo-textiles outperformed the Synthetic Geo-textiles in reduction of runoff and soil erosion. Among the Open Weave and Non Woven JGT, Open Weave JGT are more effective in reducing runoff, soil loss and nutrient loss and also increased soil moisture retention. Growth of the grass and root characters is vigorous in the plots covered by JGT as compared to Synthetic Geo-textiles. Application of Open Weave JGT increased the plant height, number of tillers, root density, surface area coverage and volume of soil binding in both the slope categories. The study concludes that the JGT can be effectively utilized for slope stabilization using the grass species as compared to Synthetic Geo-textiles. Open Weave JGT with grasses is recommended for slope stabilization in the degraded land having the slopes up to 90 %.Not Availabl

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Not AvailableEffect of sodicity on clay dispersion in salt-affected black soils of the Kabini canal command area in Chamrajnagar district, southern Karnataka was studied. Forty-eight soil samples were collected from nine soil profiles and analysed for physical and chemical properties. The clay dispersion ranged from 0.57% to 62.1%. High positive and negative correlations with exchangeable sodium and exchangeable calcium respectively, with clay dispersion were recorded, which can be predicted better with exchangeable sodium and available soil water. Based on clay dispersion value, 2%, 27% and 71% soils are dispersive, intermediate dispersive and non-dispersive respectively. Based on exchangeable sodium percentage, 50, 21 and 29 soils are dispersive, intermediate dispersive and nondispersive respectively. Application of gypsum and organics reduces the clay dispersion in surface soil. Sub-surface drainage will be more effective. Construction Of soil and water conservation structures with pile foundation; providing cement lining for soil stabilization in normal construction; providing drainage lines for the structures; construction after refilling with non-dispersive soil will save the structures in saltaffected soils.Not Availabl

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Not AvailableSoil degradation induced by erosion represents a major threat to food production and ecosystem service globally, and in India more than 80 Mha have been impacted. In the light of the serious threat, there is a pressing need for a systematic nationwide assessment of land degradation due to erosion. We discuss the potential for using caesium-137 and lead-210 tracers to address this need and the next steps to realizing nationwide implementation. Globally soil erosion has reached a level that endangers the sustainable supply of food for the growing global population. It already threatens food production and ecosystem service delivery and therefore, there is a pressing need to address this threat. This is especially true in India where, in a total area of 328 million hectares (Mha), 121 Mha is undergoing soil degradation, 68% of which is attributed to water erosion1. Water erosion rates range from 5 t ha–1 yr–1 in dense forest regions to rates in excess of 80 t ha–1 yr–1 where erosion is most severe, such as in the Shiwalik mountainous region2. India’s average soil loss has been estimated to be 15 t ha–1 yr–1; however, given the limited coverage of measurements, this should be treated with caution. In the light of the serious threat that soil erosion poses in the country, there is a pressing need for a systematic nationwide assessment of land degradation due to erosion using appropriate techniques. Following the approach adopted by the United States Department for Agriculture (USDA) and employed by other organizations, the majority of soil erosion studies in India have used run-off plot measurements2. Such studies need substantial investment timeNot Availabl